The present study summarized three studies of schema-based instruction (SBI), a research-based Tier 1 mathematics program implemented in general education classrooms. We evaluated the efficacy of SBI in improving the mathematics achievement of seventh-grade students, including students with or at risk for mathematics disabilities (MD). The three SBI studies included an overall sample of 3,846 students, some of whom were categorized as having MD and 161 teachers in 104 schools from three states, with treatment length of about 6 weeks. Teachers and their classrooms in each study were randomly assigned to either the SBI or control condition. For the overall sample, results showed that SBI students scored significantly higher and showed more linear growth over time than control students on proportional problem solving. Similar results favoring the SBI condition were also found for students with or at risk for MD. These findings suggest that SBI focused on proportional reasoning instruction is a feasible Tier 1 mathematics program for all students. We discuss implications of the SBI program for meeting the diverse needs of students in the multi-tiered systems of support (MTSS) framework and suggest future directions.